1. Field of the Invention
The present invention relates to the delivery of preheated gas into an enclosure and particularly to shaft furnaces. More specifically, this invention is directed to improved tuyere feed lines and particularly to blast furnace tuyere stocks. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
In shaft furnaces, and particularly in blast furnaces employed in the production of pig iron, preheated air is injected into the furnace via a plurality fo tuyere injection nozzles located about the periphery of the furnace. These injection nozzles are connected to a common supply pipe, located circumferentially of the furnace, by means of feed conduits which are known in the art as tuyere feed stocks. Prior art tuyere feed stocks generally consist of a number of tubular members provided with a refractory lining and connected to the supply pipe for the preheated gas by means of flanges.
In the interest of enhancing production efficiency, there has in recent years been a trend toward increasing blast furnace capacity. Increased production capacity has, to some extent, been achieved through increasing furnace pressure and temperature. Also in the interest of enhanced production efficiency, minimization of furnace shut-down time is desired and, in fact, design objectives are to enable operational periods of up to several months without the necessity of performing maintenance procedures. Accordingly, the components of the tuyere stocks, and particularly the blast nozzles and blast tuyeres which are positioned at the downstream end of the stocks adjacent the furnace wall, must be efficiently protected against the deleterious effects of hot air temperatures. To this end, the blast tuyeres, which actually project into the furnace, are typically surrounded by multi-compartmented cooling chambers. Additionally, the blast tuyeres and the blast nozzles, which are located immediately upstream of the blast tuyeres in the direction of preheated air flow, are protected by a coating of refractory material over as great a portion of their lengths as possible.
In order to compensate for and/or balance out tolerances arising during manufacture and installation, inaccuracies occurring during assembly and thermal expansion which takes place during operation, either all or certain sections of the tuyere stocks are interconnected by means of ball and socket joints, expansion bellows, pivot compensators or similar devices. Thus, by way of example, U.S. Pat. No. 3,662,696, the disclosure of which is incorporated herein by reference, describes a tuyere stock in which the joints between the individual sections of a tuyere feed line are comprised of universal coupling compensators. The construction of the patented tuyere stock offers the advantage that the various deformations in the individual sections of the feed line caused by the temperature of the gas flowing therethrough are balanced out by means of universal joints and bellows which have a limited number of undulations and which do not require the use of ball-and-socket joints. The blast nozzle of the tuyere stock of U.S. Pat. No. 3,662,696 if firmly pressed against the blast tuyere, mounted in the blast furnace wall, by means of clamping devices; the contact between the blast nozzle and the blast tuyere being in the form of a spherical sealing surface in the interest of absorbing any relative displacements between the blast nozzle and the blast tuyere.
Copending U.S. Pat. application Ser. No. 339,117 discloses a tuyere stock mount including a guide bar arrangement which prevents the blast nozzle from moving out of its central position with relation to the blast tuyere. Thus, the apparatus of U.S. Application No. 339,117 permits establishment of a rigid connection between the blast nozzle and blast tuyere. In the apparatus of copending U.S. Application 339,117 a sliding surface is provided on the bottom side of the blast nozzle while the wall of the blast furnace is provided with a guide means which cooperates with the sliding surface on the nozzle. This structure cooperates to hold the blast nozzle in the proper operating position and, if the nozzle should for any reason attempt to move relative to the blast tuyere, the nozzle is at all times kept in a central and predominantly horizontal position with respect to the blast tuyere. Additionally, clamp means are provided for pressing the blast nozzle and the blast tuyere toward the axis of the furnace and the individual parts of the tuyere stock are flexibly interconnected in such a manner that compensation for thermal expansions and constructional deviations is provided even though the lower part of the tuyere stock remains in the same position as required by the cooperation between the sliding surface of the blast nozzle and the furnace wall. The flexible interconnection of the components of the tuyere feed lines of application Ser. No. 339,117 are comprised of two universal couplings each having two diametrically opposed arms provided with slots in which the bolts of the connecting Cardan ring can slide in the longitudinal direction.
To briefly summarize the state of the art prior to the present invention, two general types of tuyere feed lines were known. A first prior art tuyere stock employs a form of pivot connection between the blast nozzle and blast tuyere whereas the other general type of prior art tuyere feed stock is characterized by the maintenance of a fixed relative position between the blast nozzle and blast tuyere. Both of these prior art approaches to the delivery of preheated gas to the interior of a shaft furnace have certain disadvantages.
Continuing with a discussion of tuyere feed lines of the type of U.S. Pat. No. 3,662,696, there is of necessity a discontinuity in the refractory lining of the blast nozzle in the vicinity of the pivot connection to the stationary blast tuyere; this pivot connection often consisting of a stainless steel ball segment as required by the high temperatures of the operating environment. In the interest of improving the operational life of this metal-on-metal joint in the face of increasing furnace temperatures, cooling means have been provided. The net effect, however, is to preclude the use of a refractory lining on the blast tuyere since such a lining would readily be eroded and destroyed as a result of the turbulence in the flowing hot air produced by the necessarily present joint gap. On the other hand, the thermal losses at the blast tuyere and the pivot joint of the blast nozzle are incompatible with the desire to increase blast temperatures; i.e., the desire to increase the temperature of the gas provided through the tuyere feed line as the temperatures within the furnace are increased. Similarly, the increases in back pressure; i.e., furnace top pressure; must be met by higher blast pressures on the blast tuyere. Higher blast pressures and gas temperatures at the blast tuyere produce operating conditions which have a deleterious effect on the operational reliability, over long periods of time, of the pivot connection of U.S. Pat. No. 3,662,696. In the patented apparatus, should withdrawal and replacement of a blast tuyere be dictated either by a component failure or the desire to perform preventative maintenance, the blast nozzle has to be disconnected from the tuyere stock and removed and thereafter the blast tuyere dislodged from its seat in the furnace wall by means of special equipment such as jolt-ramming or hammer machines. Considering the large number of blast tuyeres in a modern blast furnace, this procedure is rather time-consuming and therefore in contradiction to the desire for very short operating interruptions of the furnace.
In the case of tuyere feed lines characterized by fixed relative positioning of the blast nozzle and blast tuyere, a rather accurate adjustment of the blast nozzle/blast tuyere unit with reference to the tuyere arc cooler is required thereby demanding a special design of the various tuyere feed line elements. Nevertheless, this second general type of prior art tuyere stock is characterized by many of the disadvantages inherent to the type of stock wherein a ball joint is provided between the blast nozzle and blast tuyere.